Since the first polymer electroluminescent diode was invented in 1990, the polymer photoelectric materials have brought a widespread interest in academia and industry.
In order to achieve a high efficient polymer electroluminescent device, it is critical to inject electrons and holes high-efficiently from the cathode and the anode respectively. Therefore, many high-efficient polymer electroluminescent devices employ a multi-layer device structure, ie., in addition to the luminescent layer, comprising one or more of the hole transport/injection layer or the electron transport/injection layer. Therefore, in addition to developing an excellent luminescent material, the development of an excellent electron transport/injection material and hole transport/injection material are also critical to achieve a high-efficient polymer electroluminescent device.
The previous studies have found that the conjugated polyelectrolyte as well as its neutral precursor is a very excellent electron injection/transport material, which has a good solubility in a polar solvent and at the same time has an excellent electron transport property, so as to make it possible to manufacture a high-efficient multi-layer polymer electroluminescent device. Moreover, such material can also effectively increase the electron injection from the high work function metals (such as Al, Ag, Au) to the polymer semiconductor, further facilitating to achieve a macromolecular multi-layer device in a printing manner (Adv. Mater. 2007, 19, 810.). The subsequent studies have demonstrated that such conjugated polyelectrolyte material not only can be used in the luminescent device but also can be used as an interface modification layer so as to significantly increase the performances of the organic solar cell and the field-effect transistor.
However, most of the conjugated polyelectrolytes have free-movable counter ions, which can possibly diffuse into the luminescent layer, thus effecting the long-term stability of the device. Moreover, both the response speed of the device and the charge mobility of the conjugated polyelectrolytes are greatly influenced by the counter ions.